Does AC Bring in Outdoor Air Pollution?

It’s that time of year when Beijing is starting to sizzle, if this person roasting fish on her car is any indication. We’ve just turned our air conditioner on, and that got some in the Smart Air office wondering: does our AC suck in outdoor air pollution?


need ac in summer bring in air pollution


Although we’re roasting, air pollution doesn’t take a break during summer months:


air pollution levels during the summer


It’s not airpocalypse levels, but the buildings nearby are starting to look fuzzy.


Beijing and Delhi heat causing blurry buildings


Thus, are we faced with a choice: cool air versus clean air?


do air conditioners filter out air pollution or suck it in from outside


The short answer is no. To explain why, I’ve got three points of evidence.


1: Tests of the air coming out of the air conditioner


This test is the easiest to do. I hold up my particle counter into the stream of air coming out of my AC unit. The test shows and it’s no different from the ambient room air. (See a live AC air pollution test here). I’ve also compared that air to outside air on very dirty days, and the air coming out of the AC is nowhere near as dirty as outside air.


testing indoor air quality pollution levels when ac is turned on


air pollution levels from AC air conditioner wall mounted device


(Of course, it’s important to do this test right when turning on the AC. If I had tested the air after the AC had been running for a while, then my whole room would be dirty, not just the exhaust.)


2. Tests of the ambient room air before and after turning the AC on


Another way to test this is to test the ambient room air, not just the air coming out of the AC. To do this test, I first closed my windows and turned off my AC. I ran my particle counter for 30 minutes to get a baseline reading of indoor air pollution levels. Then I turned on the AC for 30 minutes.


Results? Air conditioners make basically no difference to indoor air pollution levels. Here’s what happened to indoor air pollution levels in one test after turning the AC on:


Do air conditioners clean air pollution


Here I’m comparing the pollution numbers just before I turned the AC on and 30 minutes later. The data shows that the AC has basically no effect on indoor air pollution levels.


Of course, any single test might not be reliable. Thus, I ran seven tests and calculated the average effect of my AC on indoor air pollution levels.


Effect of Air Conditioning on Indoor Air Quality


3. How air conditioners work


Regular wall-mounted air conditioners in China and India do have a unit outside connected with tubes to the inside. You can see those tubes on the AC in the Smart Air office in Delhi.


Wall Mounted Air Conditioner Tubes Outdoor Air


But that tube is not bringing in outside dirty air. It’s circulating coolant. So where does the air it’s blowing come from? If you look around your air conditioner, you’ll probably discover that it works like mine: it brings air from the top, runs it over the cooling coils, and blows it out the front. It’s recycling indoor air, not bringing in outdoor air.


source of air from wall mounted air conditioner


Do Central Air Systems Bring in Outdoor Air Pollution?


If you’re in a room with a central air system, things get trickier. You’ll have to do some research of your building to find out what air is coming out of those vents.


air pollution from central air system


Some systems bring in a lot of outdoor air. Some bring in none. Some systems filter that air. Some don’t.


Here’s how you can get to the bottom of it:

1. Check out the system (if you have access to it). Does it have filters? Does it have an outdoor air intake?

2. Ask the management (if they even know!).

3. Test the air coming out. Here’s how I recommend testing your central air system for outdoor air pollution.

If you don’t have a particle counter and you’re based in Beijing or Delhi, Smart Air can provide you with an indoor air quality audit to test your central air system. Smart Air also tests for general particulate air pollution and gas pollutants. 

Schedule your own indoor air quality test here!


indoor air quality audit for air conditioner and central air HVAC system

Bottom Line: Does AC Bring in Air pollution?

Wall-mounted air conditioners do not bring in outdoor air pollution. However, some central air systems do bring in outdoor air pollution.

Smart Air

Open Data: AC Air Pollution

I made the original test data available for fellow nerds here.

What Do I Know?

I’m not an expert in air pollution. I’m a social psychologist. But living through Beijing’s pollution got my nerd spirit running about air quality, and I soon got into making low-cost DIY purifiers and started a social enterprise (Smart Air) to help get low-cost purifiers to more air-breathers. With the help of dedicated nerds and volunteers, Smart Air ships simple, no-bull purifiers to air-breathers in IndiaChinaMongolia, and the Philippines.


Smart Air education



Free Guide to Breathing Safe

Want to learn more about breathing clean air? Join thousands more and stay up to date on protecting your health.

Notify of
Inline Feedbacks
View all comments
Smart Air low cost purifiers

Smart Air is a social enterprise and certified B-Corp that offers simple, no-nonsense air purifiers and provides free education to protect people from the harms of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.

Certified B-Corp air purifier company